The need for energy saving is well known. A means of doing so is to use the existing enthalpic resources and have them evolve from their present temperature to a use temperature, whilst preserving their energy content. As an example of an enthalpic resource and high temperature level, one can mention steam at 500.degree. C. from the thermal power station. The present day means of preserving the maximum energy of this resource is to use a turbine producing mechanical energy transformable into electric energy.
It can be seen that the installation requires heavy investments.
Another example is that of an enthalpic source at low temperature level (plant thermal reject, for example water at 45.degree.).
The enthalpic content of this source can be used for heating premises for example, by increasing its temperature up to 80.degree. via a heat pump.
Conventional compressed working fluid type heat pumps have a mediocre performance coefficient.
Dynamic elements (compressors) subject to wear and requiring maintenance, are needed.
Absorption pumps use a static process, but their efficiency is essentially mediocre due to the structure of their thermal cycle.
One aim of the invention is to obtain a thermal machine only involving practically reversible thermal exchanges, so as to avoid the degradation of the energy content of the thermal resources used.
Another aim of the invention is to produce a machine which, either only contains static components, so that it is sturdy and subject to very little wear, or which combines static and dynamic components, but with an energy efficiency well above that produced by systems following the known thermal cycles.
One aim of the invention is to produce a reversible thermal machine, i.e., capable of receiving thermal energy at an average temperature level and valorizing this energy by increasing it to high temperature, but also to receive energy at low and high level and supplying at an intermediate level.
Another aim is to obtain thermal devices whose manufacturing costs are notably lower as compared to thermal machines of the same power.
To clearly understand the structure and operating of the thermal device in the invention, it is necessary to recall a number of thermodynamic notions and give a certain number of definitions.
The initial idea leading to the device in the invention is that it is possible to make practically reversible static thermal transfers. This notion of practically reversible static thermal transfer originates in the study of distillation.
FIG. 1 shows diagrammatically a distilling column 1 designed to distill a mixture of two substances A and B, A being the most volatile. The column is associated to a distiller 2 and a condenser 3. The axis of the temperatures T is directed towards the bottom of the figure.
The mixture A+B is entered into the column at a temperature T.sub.2 ; substance B, of controlled purity, flows out fluid at the bottom of the column at temperature T.sub.o ; one part leaves for production P.sub.B, the other is evaporated in the distiller 2; the enthalpic content of the steam thus produced is distributed along the column; when this vapor reaches the head of the column at temperature T.sub.1, it contains substance A at controlled purity; it is then condensed; a part of A is sent to production P.sub.A, the other (reflux) is returned to the column. The arrow V shows the flow of vapor and the arrow L the flow of vapor in a section S (T) of the column and temperature T.
The physical operations involved are normally followed on the Merkel diagram; this diagram (FIG. 2) includes for each pressure:
the balanced zones, concentration x(T) liquid and y(T) vapor of substance A.
the enthalpic h (liquid) and H (vapor) of the mixture depending on the concentrations.
The correspondences between these magnitudes on the diagram are indicated in FIG. 2.
It is easy to convince oneself that the distillation thus produced cannot be reversible: by writing between two column sections the three conservation equations (flow rate A, flow rate A+B, enthalpic) it is perceived that they cannot all three be verified together; subsequently, in the conventional distillation with heat insulated columns, the liquid and vapor phases in contact necessarily evolve off balance.
The applicant has observed that to obtain the thermodynamic balance (i.e., the values of the concentrations of liquids x and vapor y corresponding to the balance at the pressures and temperatures considered), at all points, heat must be added or removed in each column section. French patent No. 80 17313 provides an example of the means that can be used to obtain reversible distillation.
The reversible distillation obtained thus is featured in this way in each specific case by a distribution of heat Q(t): ##EQU1## as shown typically in FIG. 3.
Q(T) contains several parts and notably:
part BC (exhaust E) expressing an endothermal activity of the column.
CD (rectification R) which is exothermal.
The portions BC and CD are both arcs of very taut curves which can be assimilated to straight lines, representative of exchanges with external heat-conveyance circuits with constant specific heat.
The reasoning that has been made above relating to a distiller column is applicable to all types of thermal exchanger, and in particular to a thermal system consisting for example of a packed or plate column equipped over the whole height with exchanges flowed through by external heat-conveyance circuits with sensible heat providing or extracting from the said column, the linearized heat distribution ensuring its reversible operating. A section of column equipped with an external heat-conveyance circuit with constant flow rate can be considered as an exchanger containing a first diphasic compartment, consisting of the column itself, the second compartment being flowed through by the external heat-conveyer fluid. This exchanger is referred to as heat transfer element.
It will be observed that through this exchanger the flow of energy of all the effluents remains constant depending on the temperature, to the nearest second order.
Below, thermal activity will be the term for the quantity of heat received or supplied in each thermal transfer element to ensure reversibility of the thermodynamic phenomena for each level of temperature T.
A thermal transfer element is defined by:
the nature of the diphasic mixture used
the flow rates of liquid and vapor working fluid in the first compartment
the operating pressure of the exchanger
the values of the temperatures between which the fluid evolves in the element.
The heating powers applied to the element are deduced from this (heat resources=heat contributed to the system, positive; heat uses=heat supplied by the system, negative) and subsequently the nature of the heat-conveyer.
A "reverse" heat transfer element, at another pressure, can be made to correspond to each given heat transfer element (said to be "direct"), at a given pressure, in which:
the nature of the diphasic mixture is the same as that of the heat-conveyer fluid
in the direct element and reverse element, with similar sections, the same liquid and vapor flow rates are to be found with the same concentrations of the working fluid components, but evolving in the reverse direction depending on the temperature.
the sources have the same absolute value for a direct and a reverse element, but the signs are opposite.